#include<stdio.h>
#define PI 3.14f


float area(float r)
{

    return PI*r*r;
}

int main()
{
    float r,s;
    printf("Please input the radius of your round: ");
    scanf("%f",&r);
    s = area(r);
    printf("The answer is: %.2f",s);

    return 0;
}